The inventive concepts described herein relate to an analog-to-digital converter, and more particularly, relate to a successive approximation register analog-to-digital converter.
An analog-to-digital converter may convert an analog signal into a digital signal. The converted digital signal may be transferred to other devices. A successive approximation register analog-to-digital converter (SAR-ADC) may have such a structure that one comparator is iteratively used, and may be simple in structure in that it does not include analog circuits such as a sample and hold circuit, a multiplying digital-to-analog converter (MDAC), and so on. Compared with other analog-to-digital converters, an area and power consumption of the successive approximation register analog-to-digital converter may be less. Also, the successive approximation register analog-to-digital converter may be easily applied to a low-voltage circuit.
The successive approximation register analog-to-digital converter may receive output signals of sensors to convert them into digital signals. General sensors may have single-voltage outputs. The successive approximation register analog-to-digital converter may have a single-ended input structure to convert an output signal of a sensor into a digital signal. The successive approximation register analog-to-digital converter may include SAR logic, a comparator, and a digital-to-analog converter. A differential amplifier may be used as a comparator to compare an output of a capacitive digital-to-analog converter. In this case, the successive approximation register analog-to-digital converter may perform a converting operation in a manner where an analog input voltage sampled by a capacitor is compared with level voltages generated based on a digital bit. In the case that an output range of a sensor having a single voltage output is a range (0 to Vdd) of a power supply voltage, a voltage of a node connected to a top plate of a capacitor may become higher than the power supply voltage Vdd. In this case, charge stored at a capacitor may be lost by malfunction of switches connected with a node having a voltage higher than the power supply voltage Vdd, so that the reliability of the successive approximation register analog-to-digital converter is lowered.